Device for the solar thermal gasification of starting material containing carbon

ABSTRACT

In a device for the solar-thermal gasification of carbon-containing charging material, comprising a solar reactor ( 1 ) including at least one, preferably a plurality of, light-transmissive window(s) ( 2 ) for introducing concentrated solar radiation, and a gasification chamber ( 9 ) having a preferably rectangular bottom and receiving means for the charging material ( 21 ), the receiving means are comprised of at least one, preferably elongated drawer ( 7,8,20,21,22,23 ) that is movable relative to the gasification chamber.

The invention relates to a device for the solar-thermal gasification of carbon-containing charging material, comprising a solar reactor including at least one, preferably a plurality of, light-transmissive window(s) for introducing concentrated solar radiation, and a gasification chamber having a preferably rectangular bottom and receiving means for the charging material.

The solar-thermal gasification of carbon-containing charging material serves to thermally decompose various starting products under controlled atmosphere for the production of a synthesis gas and is, for instance, described in CH 692927 A5, WO 2008/027980 A1, or the article by P. v. Zedtwitz, A. Steinfeld: “The solar thermal gasification of coal—energy conversion efficiency and CO₂ mitigation potential” in Energy 28 (2003) 441-456. Typical for solar-thermal gasification is that the radiation energy of an external source, preferably concentrated solar energy, is used for the generation of the process heat required for the gasification reaction.

Broadly speaking, a gasification reaction takes place in a solar reactor in the presence of water vapor according to the equation CH_(x)O_(y)+(1-y) H₂O->CO+(1+x/2−y)H₂ and in the presence of carbon dioxide gas according to the equation CH_(x)O_(y)+(1−y)CO₂->(2−y)CO+(x/2)H₂. These equations are, however, a rough simplification of the actually prevailing conditions, wherein, in detail, the following reactions are of particular relevance: The vapor gasification according to the equation C_((gr))+H₂O×CO+H₂ is, of course, superimposed by the Boudouard equilibrium according to the equation 2 CO=C_((gr))+CO₂ as well as side reactions in which methane is, for instance, formed from carbon according to the equation C_((gr)+)2 H₂=CH₄. A reforming reaction proceeds according to the equation CH₄+H₂O=CO+3H₂, wherein a shift of the CO/CO₂ equilibrium can finally also be achieved by water vapour, of which the following equation is characteristic: CO+H₂O=CO₂+H₂. At temperatures of below 550° C., graphite, methane, CO₂ and H₂O are thermodynamically stable. It is only at significantly higher temperatures that a substantially uniform phase of H₂ and CO will be achieved. In this respect, temperatures of 1000° C. and 1300° C. are preferred, on the one hand because of the reaction rate increasing with rising temperatures, and on the other hand also because of the thermal decomposition of tar-forming compounds possibly present in the charging material, which will not be ensured below said temperature range.

The quality of the obtained synthesis gas is, of course, substantially determined by the ratio of H₂ to CO, and the ratio of CO₂ to CO. A shift of the ratio of H₂ to CO can be achieved in a particularly simple manner at temperatures of 250 to 450° C. using water vapour (water gas shift). Another gasification option is the use of a mixture of H₂O and CO₂ so as to influence the ratio of H₂ to CO. Coal, biomass and various carbon-containing waste materials such as contaminated soils, sewage sludges, filter residues and the like have been proposed amongst others as charging materials for solar-thermal gasification.

Carbon-containing wastes are frequently used as inferior, secondary fuels for the operation of clinker or cement kilns. However, the use of such inferior fuels involves a number of disadvantages. Thus, the replacement of high-quality coal with inferior fuels will, for instance, result in a decrease of the adiabatic flame temperature in the sinter zone or main firing from 2300° C. to temperatures below 1900° C., major drawbacks in the clinker process being already observed at temperatures below 2100° C. A decline of the flame temperature by 200 to 300° C. due to the use of inferior fuels and, in particular, the use of alternative fuels will result in a less favorable temperature profile over the longitudinal axis of the rotary kiln and, as a rule, will cause the temperature maximum, which would ideally extend over a short region, to extend over an extended region at a reduced temperature. The thus observed deterioration of the quality of clinker primarily relates to the reactivity of clinker.

WO 2009/090478 A2, therefore, has already proposed to subject carbon-containing waste materials to solar-thermal gasification and feed the thus obtained high-quality synthesis gas to the burners of the main firing system of a clinker kiln in order to increase the flame temperature. In that the gasification is performed by applying radiation energy, any contamination due to combustion exhaust gases as in autothermal gasification processes will be avoided, and the energy content of the synthesis gas will be increased due to the absorbed radiation energy such that a substantially higher-quality synthesis gas characterized by a small amount of combustion gas per energy unit will be obtained. This synthesis gas is, therefore, suitable for raising the flame temperature and can be fed to the burners in appropriate partial quantities so as to improve the clinker process and the temperature profile in the clinker kiln.

For large-scale use such as in the context of the utilization of waste materials in clinker production, the difficulty is to provide solar reactors having appropriately large capacities. Fluidized bed reactors are unsuitable for lumpy materials, since their use would involve high crushing expenditures. For large capacities they are also ruled out because of constructional reasons, so that structures with stationary material beds will have to be used. In this respect, it will, in particular, be necessary to distribute the charging material on as large a surface as possible while minimizing the bed height, and to find ways to charge the reactor with material in a simple manner and in as short a period of time as possible and subsequently discharge the ashes just as simply and rapidly.

The present invention, therefore, aims to further develop a device of the initially defined kind to the effect that the above requirements will be met.

To solve this object, the invention in a device of the initially defined kind provides that the receiving means are comprised of at least one, preferably elongated drawer that is movable relative to the gasification chamber. In a preferred manner a plurality of adjacently arranged, preferably elongated drawers that are movable along parallel displacement paths are provided. The drawer(s) serve to receive a stationary material bed and, considering the limited structural height of the solar reactor of, for instance, 1 meter, can be designed accordingly flat. The at least one drawer preferably has a height between the bottom and the upper edge of the side walls of less than 50 cm, in particular less than 40 cm. The material bed may, for instance, have a maximum thickness of 35 cm in order to ensure that the material will be gasified over the entire material thickness on the same day. A layer thickness that is too large might involve the risk of an insulating ash layer forming on the upper side of the material bed, which would prevent the gasification of the residual amount located therebelow.

In that the at least one drawer is movably arranged, it can be easily pulled out from the solar reactor and pushed back into the same. This allows the loading and unloading of material to be performed outside the solar reactor, i.e. outside the gasification chamber, so as to avoid that loading and unloading devices plus operating personnel would have to enter the gasification chamber, which is difficult to accede because of its low structural height and, moreover, infiltrated with a hot and toxic atmosphere. The configuration in this context is preferably devised such that the at least one drawer is displaceable between a loading and unloading position outside the gasification chamber and an operating position within the gasification chamber.

In order that the interruption of the gasification process caused by the loading and unloading of the at least one drawer is kept as short as possible, it is preferably provided that a first and a second drawer are each coupled to each other and consecutively arranged in the longitudinal direction such that the first drawer is in the operating position when the second drawer is in the loading and unloading position, and the second drawer is in the operating position when the first drawer is in the loading and unloading position. This enables a drawer to be unloaded and reloaded while the other drawer is in the gasification chamber. Sufficient time will thus be available for the unloading and subsequent loading procedures so as to enable sufficient cooling of the drawers and the safe removal of the ash remaining after the gasification process. A further advantage resides in that, if required, maintenance of the drawers will be possible in the loading and unloading position without having to interrupt the gasification process.

In order to avoid environmental impairments by possibly spilt charging material, a loading and unloading building is preferably each arranged on both sides of the solar reactor, into which the drawers can be moved to assume the loading and unloading position. In order to automate loading and unloading, it is, moreover, preferably provided that a plurality of loading and/or unloading devices each overlapping the drawers in a gantry-like manner and being movable in the longitudinal direction of the drawers are arranged in the loading and unloading buildings. The loading and unloading buildings are, in particular, closed buildings in order to enable the interiors of the buildings to be controlled in terms of temperature conditions and gas composition of the atmosphere. This will enable controlled cooling of the drawers pushed out of the gasification chamber, and controlled deaeration and aeration of the buildings so as to enable the gases eventually escaping from the ashes to be drawn off.

In order to maximize the receiving capacity of the drawers without hampering their mobility, it is preferably provided that the drawers are designed to be elongated with the longer extension in the direction of movement. With appropriately dimensioned solar reactors, lengths of, for instance, 10-40 m, preferably 20-40 m or more, can thus be implemented.

According to a preferred further development, a good movability of the at least one drawer will be ensured in that guide means, in particular rails, are provided for guiding the at least one drawer along a displacement path.

In order to enable vapor gasification in a simple manner, the drawers each preferably have a bottom with openings for feeding water vapor. In a particularly preferred manner, said openings connect the gasification chamber to a distribution chamber integrated in the drawer and disposed below the bottom.

As already mentioned above, the irradiation of the concentrated solar radiation into the solar reactor occurs via at least one light-transmissive window. Taking into account the high temperatures involved, the at least one window is preferably made of quartz. The light-transmissive window(s) are each preferably associated with a beam focusing device to achieve the required concentration of the solar radiation. Beam concentration can, for instance, be performed using a CPC (compound parabolic concentrator).

In general, it should be made sure that the window(s) will not be contacted by the gaseous decomposition products of the gasification reaction, since these might attack the material of the window(s). A preferred further development, therefore, contemplates that the solar reactor above the gasification chamber comprises a further chamber, into which the concentrated solar radiation enters through the at least one light-transmissive window. The concentrated solar radiation thus reaches the gasification chamber not directly, but via said further chamber. Due to the direct irradiation into said further chamber, an immediate temperature increase is to be observed in the latter, the heat transfer into the gasification chamber taking place via the ceiling of the gasification chamber. A preferred configuration in this context contemplates that the gasification chamber and said further chamber are separated from each other by a ceiling composed of high-temperature-resistant plates. The high-temperature-resistant plates will act as radiation elements or radiation plates irradiating the thermal energy into the gasification chamber.

Said plates, as a rule, are only available in defined dimensions and cannot be designed at will, wherein an appropriate support structure should be provided. In this respect, a carrying structure is preferably provided for the high-temperature-resistant plates, comprising support means for supporting the carrying structure, which are arranged between the drawers. The support means, in particular, comprise partition walls extending on the bottom of the gasification chamber between the drawers and ending at a distance from the ceiling. The support means preferably comprise support columns supported on the partition walls and carrying the carrying structure.

In operation, temperatures up to 1,300° C. prevail in the gasification chamber. Correspondingly temperature-resistant or refractory materials are, therefore, required. In particular, it is to be avoided that metal parts are exposed to the radiation energy and/or the high temperatures. The radiation plates separating the gasification chamber from said further chamber, therefore, are preferably made of graphite, preferably with a SiC coating. The support columns are preferably made of SiC (silicon carbide). The drawers may be made of steel and lined with a suitable refractory material.

In order to enable the at least one drawer to be moved to and fro between the operating position and the loading and unloading position, a closeable opening is preferably each provided on two opposite sides of the solar reactor. The pushing in and out of the drawers involves the risk of ambient air escaping into the gasification chamber, which might cause a fire. Such a risk will be particularly high if, as is preferably provided, a negative pressure exists in the gasification chamber relative to the surrounding areas. In order to minimize the entrance of false air into the gasification chamber, the opening is preferably associated with a sluice-like device, e.g. a curtain, in particular a metal curtain.

In the following, the invention will be explained in more detail by way of exemplary embodiments schematically illustrated in the drawing. Therein,

FIG. 1 is an overall view of a device according to the invention;

FIG. 2 is a detailed illustration of a cutout of FIG. 1;

FIG. 3 is a schematic illustration of the drawer arrangement in a device according to FIG. 1;

FIG. 4 depicts an unloading device in side view;

FIG. 5 depicts a loading device in side view;

FIG. 6 is a front view of the loading device according to FIG. 5;

FIG. 7 shows the device according to the invention in a reduced configuration;

FIG. 8 depicts the gasification chamber of the device according to FIG. 7; and

FIG. 9 is a cross-sectional view of the device according to FIG. 7.

In FIG. 1, a solar reactor is denoted by 1, which, on its upper side, comprises a plurality of windows 2 through which concentrated solar radiation can be introduced into the interior of the solar reactor 1. In order to concentrate said radiation, a plurality of beam-focusing devices 3 are provided, into which solar radiation enters from top in the sense of arrows 4. The incident radiation is concentrated in the center and at the exits of the beam-focusing devices 3 by being reflected by parabolic or approximately parabolic surfaces, and enters the solar reactor 1 via the windows 2. The solar reactor 1 is adjoined on both sides each by a loading and unloading building 5 and 6, respectively, in which drawers 7 and 8, respectively, to be explained in more detail below are loaded with material and unloaded. In the position illustrated in FIG. 1, the drawer 7 is in the loading and unloading building 6 and the drawer 8 is in the solar reactor 1.

In FIG. 2, the detail denoted by II in FIG. 1 is illustrated on an enlarged scale. It is apparent that the solar reactor comprises two chambers, i.e. a chamber 10 into which the concentrated solar radiation enters via the windows 2, and a gasification chamber 9, which is sufficiently gas-tightly separated from the chamber 10 by a ceiling 11, in which the solar-thermal gasification of the charging material 12 is performed using the thermal energy irradiated from the chamber 10. The external insulation of the solar reactor 1 is denoted by 13. The charging material 12 is received within the gasification chamber in the drawer 8 in the form of a material bed, said material bed preferably resting on a gravel bed 14 to protect the drawer 8. In the bottom of the drawer 8 is provided a distribution chamber 15 capable of being filled with water vapor and/or CO₂ gas, said water vapor and/or CO₂ gas being feedable through connection 16. The bottom of the drawer 8 is provided with a perforated plate, through which the water vapor and/or CO₂ gas present in the distribution chamber 15 can escape. The perforated plate preferably extends over the entire bottom surface of the drawer 8 so as to enable a nearly uniform exposure of the material bed to water vapor and/or carbon dioxide gas.

The drawer 7, which is in the loading and unloading position, is identically designed as the drawer 8. To move the drawers 7, 8 between the operating position and the loading and unloading position, the solar reactor 1 is provided with an opening 17, which is closed in operation by a vertically movable gate 18 and opened after completion of the gasification process. Guide rails 19 are provided to guide the drawers 7, 8 along the displacement path.

From FIG. 3 it is apparent that a plurality of drawers are adjacently arranged in the solar reactor 1, two drawers each being consecutively arranged in the longitudinal direction and connected to each other. In FIG. 3, only some of the drawers are illustrated, namely the interconnected drawers 7 and 8, 20 and 21, 22 and 23, wherein, of the two interconnected drawers, one is each in the operating position, i.e. within the gasification chamber 9, and the other is in the loading and unloading position, i.e. within one of the two loading and unloading buildings 5 and 6, respectively. The other drawers are not illustrated for the sake of clarity. It is, however, possible to use so many drawer pairs that the entire surface of the solar reactor 1 will be utilized. By way of the example of drawers 22 and 23, a cable winch 24 is provided as a displacement drive for a drawer pair, said cable winch being anchored to the building 5 by an anchorage 25.

As illustrated in FIG. 3, the drawers are advantageously arranged in such a manner that the drawers of adjacent drawer rows, which are each in the loading and unloading position, are positioned in different loading and unloading buildings. In other words, the drawer that is in the loading and unloading position, of every second drawer row is positioned in the loading and unloading building 5 and the respective drawer of the respectively intermediately located drawer row is positioned in the other loading and unloading building 6. This will ensure that a spacing will remain between the drawers arranged in the respective loading and unloading building 5 and 6, respectively, so as to facilitate the loading and unloading of the individual drawers.

The described drawer arrangement allows for a nearly interruption-free mode of operation of the solar reactor 1 during the day. While the charging material present in the drawers 8, 20 and 22 is being gasified in the gasification chamber, the ashes derived from a preceding gasification process, which are present in drawers 7, 23 and 26, can be removed using unloading vehicles, and the drawers 7, 23 and 26 can subsequently be filled with new material using loading vehicles 26. After completion of the gasification process, the drawers 20 and 22 are moved into the loading and unloading building 6 and the drawer 8 is displaced into the loading and unloading building 5, the respectively coupled drawers 7, 23 and 26 entering the solar reactor 1 simultaneously to start a new gasification process. At the same time, the drawers 8, 20 and 22 are unloaded in the respective loading and unloading building 5 or 6, and subsequently reloaded. The described sequence may be repeated as many times as desired.

FIG. 3, moreover, depicts a gas flue 27 connected to the gasification chamber 9 of the solar reactor 1, which gas flue serves to draw off the false air entering the gasification chamber 9 during the displacement of the drawers between the operating position and the loading and unloading position.

FIG. 4 depicts the unloading vehicle 28, which serves to unload, or collect, the ash remaining in the drawer 21 after the gasification process. To this end, the vehicle 28 comprises a proboscis 29 which, on its end, carries a nozzle extending over the width of the drawer. The vehicle 28 comprises a track exceeding the width of the drawer and is, therefore, able to be positioned with its suction nozzle above the drawer (as illustrated in FIG. 6 by way of the loading vehicle 26) and move along the drawer in the longitudinal direction. The vehicle 28 comprises a collecting tank for collecting the aspirated ash.

FIGS. 5 and 6 depict the loading vehicle 26, which comprises a storage tank for the charging material to be applied, and a material distribution device for uniformly applying the material over the entire width of the vehicle. In a preferred manner, such application is effected by a driven conveyor means whose drive is coupled to the moving drive of the vehicle 26 such that the, amount applied will be proportional to the moving speed of the vehicle. As is apparent from FIG. 6, the track width of the vehicle exceeds the width of the drawer 21, which results in a structure overlapping the drawer in a gantry-like manner.

FIG. 7 illustrates a reduced configuration of the solar reactor 1, whose gasification chamber 9 merely receives two drawers 8′ and 20′. However, apart from this, the configuration according to FIG. 8 corresponds to the configuration according to FIGS. 1 to 3. The drawers are illustrated in the empty state, and it is apparent that the bottoms of the drawers each comprise a plurality of openings 33 like a perforated plate, through which water vapor and/or carbon dioxide gas can escape from the distribution chamber 15. The bottoms of the drawers, moreover, carry screen-like subdivisions 31 forming a plurality of flat troughs for receiving the gravel bed 14.

From FIG. 7 it is apparent that the top 30 of the solar reactor is designed to be segmented. Furthermore, openings 32 opening into the gasification chamber 9 are illustrated, which serve to feed carrier or flush gas.

In FIG. 8, only the lower part of the solar reactor 1, i.e. the gasification chamber 9, is illustrated. There, the discharge opening 34 for drawing off the synthesis gas forming during the gasification reaction can be seen. The discharge opening 34 is located above the drawers in the hot reactor space. This will safeguard that possibly tar-forming substances emerging from the material to be gasified will be thermally decomposed into non-tar-forming synthesis gas components like CO, H₂, etc. prior to leaving the reaction space. Furthermore, a partition wall 36 is provided between the two drawers 8′ and 20′, which partition wall carries support columns 37 which, in turn, carry a grid-shaped carrying structure 35. As illustrated in FIG. 9, the carrying structure 35 serves to support high-temperature-resistant plates 38 forming the ceiling 11. 

1-15. (canceled)
 16. A device for the solar-thermal gasification of carbon-containing charging material, comprising a solar reactor including at least one light-transmissive window for introducing concentrated solar radiation, a gasification chamber having a preferably rectangular bottom, and a further chamber into which the concentrated solar radiation enters through the at least one light-transmissive window, the further chamber arranged above the gasification chamber; a beam focusing device associated the at least one light-transmissive window for concentrating solar radiation; and receiving means for charging material into the gasification chamber, wherein the receiving means comprises at least one drawer that is movable relative to the gasification chamber.
 17. A device according to claim 16, wherein said receiving comprises a plurality of adjacently arranged drawers that are movable along parallel displacement paths.
 18. A device according to claim 16, wherein said receiving means comprises at least one drawer displaceable between a loading and unloading position outside the gasification chamber and an operating position within the gasification chamber.
 19. A device according to claim 16, wherein said device further comprises guide means, in particular rails, for guiding the at least one drawer along a displacement path.
 20. A device according to claim 18, wherein the at least one drawer has a bottom with openings for feeding water vapor and/or carbon dioxide gas.
 21. A device according to claim 20, wherein said openings connect the gasification chamber to a distribution chamber integrated in the drawer and disposed below the bottom.
 22. A device according to claim 16, wherein said device further comprises a ceiling to separate the gasification chamber and the further chamber from each other, the ceiling comprising high-temperature-resistant plates.
 23. A device according to claim 22, wherein said device includes a carrying structure for the high-temperature-resistant plates that comprises support means for supporting the carrying structure, which are arranged between the drawers.
 24. A device according to claim 23, wherein the support means comprises partition walls (36) extending on the bottom of the gasification chamber (9) between the drawers and ending at a distance from the ceiling (11).
 25. A device according to claim 24, wherein the support means further comprises support columns supported on the partition walls and carrying the carrying structure.
 26. A device according to claim 18, wherein said device includes a first and a second drawer that are coupled to each other and consecutively arranged in the longitudinal direction such that the first drawer is in the operating position when the second drawer is in the loading and unloading position, and the second drawer is in the operating position when the first drawer is in the loading and unloading position.
 27. A device according to claim 18, wherein solar reactor is arranged in between adjacent buildings provided for loading and unloading the drawers, wherein the drawers can be moved from an operating position within the gasification chamber to at least one of the buildings and a loading and unloading position.
 28. A device according to claim 27, wherein a plurality of loading and/or unloading devices, each overlapping the drawers in a gantry-like manner, are movable in the longitudinal direction of the drawers and are arranged in the buildings.
 29. A device for the solar-thermal gasification of carbon-containing charging material comprising: a solar reactor having a gasification chamber having a rectangular bottom, a further chamber arranged over the gasification chamber, a separator arranged between the further chamber and the gasification chamber to separate and to transfer thermal energy from the further chamber to the gasification chamber, a light-transmissive window in the solar reactor through which concentrated solar radiation can be introduced into the further chamber of the solar reactor, and a beam focusing device for concentrating solar radiation, wherein the beam focusing device is associated with the light-transmissive window; and receiving means for introducing the carbon-containing charging material into the gasification chamber, the receiving means comprising at least one elongated drawer that is movable relative to the gasification chamber and is displaceable from an operating position within the gasification chamber to a loading and unloading position outside the gasification chamber.
 30. A device according to claim 29, wherein the device includes a plurality of light-transmissive windows and a plurality of beam focusing devices.
 31. A device according to claim 30, wherein the receiving means comprises a plurality of elongated drawers. 